High frequency communication systems, which employ ionospheric channels for point-to-point communications, are subject to a number of transmission quality degradation characteristics, such as multipath propagation and Doppler spread, and often suffer from fading or temporary loss of signal. To accommodate for these effects and hopefully maximize the probability of conducting a successful transmission between two stations, particularly in the case of multistation, or multinode, networks, a plurality or pool of frequencies is made available to the member stations of the network and communications are established by assigning to a pair of stations who wish to communicate with one another a frequency that has been determined to possess some defined probability of throughput success. Often this task has been accomplished by a trial and error process of manually tuning a station transceiver to the different frequencies of the pool until a frequency that `get's through` is found. Even in those cases where station equipment contains a scanning receiver, the step and wait process carried out by the transmitting site and the types of waveforms used to confirm signal acquisition have made for such a slow process that communication channel set-up times on the order of ten to twelve minutes are not uncommon In addition, because the frequency management process employs signal protocols that require very high signal-to-noise ratios (typically on the order of 10-20 dB), channels that would otherwise be available for use by the network may be buried (and therefore unlocatable) in the presence of noise (which is non-Gaussian in an H.F. channel).
For an illustration of examples of literature describing a variety of conventional frequency management schemes, attention may be directed to the following: U.S. Pat. Nos. 3443228, 3887798, 4023103, 4066964, 4140973, 4146839, 4155040, 4193030, 4197500, 4271524, 4291409, 4309773, 4320514, 4328581, 4355399, 4365338, 4388726, 4555806 and 4616364, European Patent No. 182762 and Soviet Union Patent Nos. 562928, 612415 and 1053302 and an article by J. J. Merkel et al entitled "Microcomputer Application to a Spread Spectrum Frequency Hopping Modem", National Telecommunications Conference, San Diego, CA. 1974, PP. 536-542.